The present invention relates to a method of replicating a microstructure of a metal alloy part. More particularly, the present invention relates to an inspection method for determining a presence of incipient melting in a metal alloy part, such as those used in an aircraft engine.
Metal parts may be prone to developing cracks, especially when exposed to extreme conditions. For example, a gas turbine engine operates at extreme temperatures and pressures. Many of the engine parts may be made of nickel-based alloys and other high temperature alloys that are able to withstand the high operating temperatures. Even when high temperature alloys are used, the engine parts (such as, for example, vanes) may crack. A repair process for a vane within an assembly includes filling the cracks with a metal alloy and then heat treating the vane assembly. This repair process, known as a braze alloy repair, commonly lowers an incipient melting temperature of the base metal alloy that forms the engine part. This is because the braze alloy material contains boron, which acts as a melting point suppressant, so the braze material melts at a lower temperature and is able to fill the cracks in the base metal alloy. As a result of a diffusion of boron into the base metal alloy, incipient melting of the base metal alloy may occur during the repair process. After a melted area of the metal alloy then cools and re-solidifies, voids or pores form in a microstructure of the metal alloy, which compromises the integrity of the metal alloy part.
In some cases, once a part has undergone one braze repair and returned to service, the part may not be repaired again once it is removed from service a second time. This is due, in part, to the risk that incipient melting may have occurred during the first crack repair. The part is thus deemed non-repairable, and in some cases, may be scrapped after it is removed from operation. In other cases, the part may be permitted to undergo a second, or even a third, braze repair. However, the part must first undergo expensive and lengthy testing, which includes an evaluation to determine if incipient melting has occurred, in which case the part likely should not undergo an additional repair.
There is a need for an improved method of inspecting metal alloy parts for incipient melting to easily and economically determine if a part is in a condition to undergo a braze repair and be returned to service.